I've been watching this one on GB. It ends soon. I was interested because it was listed as a 1960, but I've decided to search for a WMR only 1960.
The one you are looking at on Gunbroker is a Ruger (RSSMXW) Single-Six WIN, .22RF MAG. CAL. which is roll marked on the frame. It was shipped with the EXTRA .22LR Cylinder which should be etched with the last 3 of the S/N on the face of the cylinder.
Not quite sure what you are looking for when you state WMR unless you mean a MAG marked without being shipped with the extra 22 LR Cylinder. My Question would be WHY???
The S/N range for Mag. Marked SS for 1960 is 305543---318695
The RSSMXW S/N 317276 on the bottom left is a 1960 with the extra 22LR Cyl. and XR3 grip frame The RMSSR bottom right is 1959 WO extra Cyl and XR3 frame with rubber grips. There are 5 variations of the Mag Marked RSSM in the picture.
Single-Six Convertible RSS5X XR3 Grip frame
Single-Six RSS4 and RSS5 with XR3 grip frames
The two at the top were not shipped with extra mag cyl. and are 22LR only BUT they have a 22 Mag. bore.